The Algonquin in Northern Quebec just wash and scrape the moose hide, and they use soap. They might cook and eat the brains but they don't use them for tanning.
After they have fleshed the hide and took the hair off they they smoke it over a smoldering cedar punk fire so that it will stay soft after it gets wet.
They smoked it by making it into a little wigwam over the smoldering punk that was in a pit. They smoked it until the smoke came all the way through the hide from the inside out. The punk was the kind of rotted cedar wood that breaks into little square cubes.
After that they work it to break the fiber of the hide.
Hide breaking is not really about scraping. It is pushing and working the hide as it dries so that the fibers in the hide stay loose. The used blunt tools like paddles instead of sharp tools.
Sometimes they used stone or wooden clubs to beat the hide with glancing blows, just enough to stretch and loosen it.
As the hide dries the creosote and aldehydes from the smoke combine with the protein of the hide and preserve it. The tars from the smoke water proof the hide so it does not go stiff if it gets wet and dries out again.
The major aldehyde in the smoke that tans the leather is formaldehyde (H2CO). It bonds to and makes and cross links with the protein fibers in the hide.
(I am not sure about what other chemicals are in the smoke or just how they work, I assume it is complicated)
Here is a link that tries to describe the natives further north tanning with almost the same method.
( From NWT tourism.)http://www.nwtarts.com/pdf/tannedhides.pdf
The NWT pamphlet is wrong about the smoking fire.
You don't want hot coals at all.
You want slow smoldering cedar punk only.
It is like cold smoking fish.
If you get heat you will cook the hide instead of curing it.
Not all tribes or families converted everything into buckskins.
In the far north they also tanned with Alder bark. Hemlock is a very good source of tannic acid too, maybe even better than Red Oak.
One reason some people used brains, marrow or even the tallow from around the kidneys sometimes, was to get oil into the hide and lubricate it.
With bark or chemical tanned hides we use either neet's foot oil or sulphated mineral oil.
Otherwise the leather is like cardboard, hard, brittle and likely to break instead of bend.
Another good tanning chemical is gluteraldehyde. It will tan a hide pure white but it is not natural at all. Leather made with gluteradehyde is so stable that it can be washed in hot water and not cook.